In one oven, the Cardinals burn their hand-written ballots, so the choice for Pope remains a secret. In the other, a chemical concoction is burned, sending the correct color smoke out the chimney that the world watches.

“The result is requested by means of an electronic control panel and lasts for several minutes while the ballots are burning in the other stove,” said the Vatican Information Service.

Black smoke is made from potassium perchlorate, anthracene, and sulphur. The white smoke is a mixture of potassium chlorate, lactose, and rosin. The rosin is a natural amber resin obtained from conifers (pine).

Prior to 2005, the black smoke was obtained by using smoke black or pitch and the white smoke by using wet straw. Often the results were difficult to ascertain, or the smoke generated from the burning ballots would overwhelm the purposefully generated smoke.

“A lot of time smoke can give tell-tale signs of what’s burning,” said Deputy Chief Perry Ebner, the Minneapolis Fire Marshall. “If it’s very black, a lot of contents are burning.”

We see black smoke when there’s a lot of little carbon particles in the air. That happens when there’s “incomplete combustion,” Ebner said.

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